hi mate good effort on taking her in... there is a couple around here who have ferret rescue and the under nurished ones they take in they feed them thin strips of cooked chicken for a few wks then get them on bigger stuff, put a bit of raw egg in the dish every other day for a wk aswell will soon get back to weight, mine was under the weather and didnt eat for over a wk due to losing his buddy but a bit of time and effort he is back and big... good luck pal